Effects of estradiol and progesterone on calcitonin secretion

Age-Related Changes in Calcitonin-Producing Thyroid C-Cells of Male Wistar Rats

Thyroid C-cells secrete the hormone calcitonin (CT) which acts as an inhibitor of bone resorption. Our aim was to examine the age-related changes in the structure and function of CT-producing C-cells, using histomorphometric, ultrastructural, and biochemical analyses. We used young adult (3-months-old), middle-aged (16-months-old), and old (24-months-old) male rats. The peroxidase-antiperoxidase method was applied for localization of CT. Stereological analysis was performed using the newCAST stereological software package. Serum samples were analyzed for the determination of CT, testosterone (T), calcium (Ca2+), and phosphorus (P). We found a significant increase in the volume density (Vv) of C-cells in both older groups (p < 0.05). The percentage of smaller volume range C-cells increased (p < 0.0001), while the proportion of greater volume range C-cells decreased (p < 0.05) with ageing. Ultrastructural analysis revealed a larger number of secretory granules in older rats. Serum CT increased (p < 0.001), while serum T and P were reduced (p < 0.01) in older rats. Serum Ca2+ was lower (p < 0.0001) in middle-aged rats compared to young adults. We revealed a 20% incidence of C-cell hyperplasia in older rats and one case of medullary thyroid carcinoma in an old rat. Our findings indicate that the ageing process causes significant histomorphometric changes at the thyroid C-cell level.

Response of trabecular bone, thyroid C and follicular cells to synthetic salmon calcitonin in middle-aged orchidectomized male rats

In contrast to studies in women, male osteoporosis is poorly understood and strictly related to advancing age. Among the first antiresorptive substances used in the prevention and treatment of osteoporosis is calcitonin (CT), a hypocalcemic hormone that potently inhibits osteoclastic bone resorption. Natural CT is produced and secreted by thyroid C-cells. The other endocrine population of thyroid cells produces thyroid hormones (TH), which also affect bone turnover. The aim of this study was to evaluate the influence of salmon CT on trabecular bone microarchitecture with special reference to effects on the structure and function of both CT- and TH-producing thyroid cells in orchidectomized (Orx) middle-aged rats. Twenty-four male Wistar rats aged 15 months were randomly divided into Orx and sham-operated (SO) groups. One group of Orx animals received (s.c.) synthetic salmon CT (Orx + CT; 100 IU kg-1 b.w.) subcutaneously every second day for 6 weeks. The second Orx group and SO rats were given the same volume of vehicle alone by the same schedule. Trabecular bone histomorphometrical parameters were: cancellous bone area (B.Ar), trabecular thickness (Tb.Th), trabecular number (Tb.N) and trabecular separation (Tb.Sp) were obtained with an ImageJ public-domain image-processing program. The peroxidase-antiperoxidase method was applied for localization of CT in C-cells. Anti-human CT antisera served as the primary antibodies. For immunohistochemical characterization of vascular endothelial growth factor (VEGF) in thyroid tissue, rabbit antisera against human VEGF, served as primary antibodies. CT-immunopositive thyroid C-cells, thyroid follicular epithelium, interstitium and colloid were evaluated morphometrically. Blood serum samples were analyzed for CT, osteocalcin (OC), and thyroxine (T4 ), and calcium (Ca2+ ) concentration was determined in urine samples. Salmon CT application significantly increased B.Ar, TbTh and TbN, but markedly decreased Tb.Sp. Administration of exogenous CT significantly decreased mean volume (Vc) and relative volume density (Vv) of thyroid C-cells in relation to both SO and Orx groups. The Vv of the colloid was higher, whereas the VV of the follicular epithelium was lower after CT treatment compared with Orx alone. CT treatment markedly elevated serum CT, whereas serum OC, T4 and urinary Ca2+ concentrations were lower than in the Orx group. These results indicate that salmon CT stimulates trabecular bone microarchitecture, strongly inhibits thyroid C-cells and changes the structure of the thyroid gland, indicating hypoactivity.

Physiology, production and action of progesterone

INTRODUCTION

The aim of this article is to review the physiology of progesterone and focus on its physiological actions on tissues such as endometrium, uterus, mammary gland, cardiovascular system, central nervous system and bones. In the last decades, the interest of researchers has focused on the role of progesterone in genomic and non-genomic receptor mechanisms.

MATERIALS AND METHODS

We searched PubMed up to December 2014 for publications on progesterone/steroidogenesis.

RESULTS AND CONCLUSIONS

A better understanding of the biological genomic and non-genomic receptor mechanisms could enable us in the near future to obtain a more comprehensive knowledge of the safety and efficacy of this agent during hormone replacement therapy (natural progesterone), in vitro fertilization (water-soluble subcutaneous progesterone), in traumatic brain injury, Alzheimer's disease and diabetic neuropathy, even though further clinical studies are needed to prove its usefulness.

Tamoxifen stimulates calcitonin-producing thyroid C-cells and prevents trabecular bone loss in a rat model of androgen deficiency

Thyroid C-cells produce calcitonin (CT), a hypocalcemic hormone, that acts as an inhibitor of bone resorption. In this study, we investigated the effects of tamoxifen (TAM) as a selective estrogen receptor modulator on thyroid C-cells, trabecular bone and biochemical markers of bone metabolism in an animal model of androgen deficiency, represented by middle-aged orchidectomized (Orx) rats. Fifteen-month-old male Wistar rats were divided into: Orx and sham-operated (SO) groups. Rats from one Orx group were injected subcutaneously with TAM citrate (Orx + TAM; 0.3 mg kg(-1) b.w.), while the rats from SO and a second Orx group received vehicle alone, once a day for 3 weeks. The peroxidase-antiperoxidase method was applied for localization of CT in C-cells. Thyroid C-cells were morphometrically and ultrastructurally analyzed. An ImageJ image-processing program was used to measure bone histomorphometric parameters. Blood serum samples were analyzed for CT, osteocalcin (OC), calcium (Ca2+ ) and phosphorus (P). Urinary Ca2+ concentrations were measured. TAM treatment significantly increased thyroid C-cell volume (Vc ) and serum CT when compared with vehicle-treated Orx rats. Analysis of trabecular microarchitecture of the tibia showed that administration of TAM significantly increased cancellous bone area, trabecular thickness and trabecular number, whereas trabecular separation was significantly decreased compared with vehicle-treated Orx rats. Serum OC and urinary Ca2+ concentrations were significantly lower in comparison with the control Orx group. These results indicate that in our rat model of androgen deficiency, TAM stimulated calcitonin-producing thyroid C-cells and increased trabecular bone mass.

The effects of sex steroids on thyroid C cells and trabecular bone structure in the rat model of male osteoporosis

Androgen deficiency is one of the major factors leading to the development of osteoporosis in men. Since calcitonin (CT) is a potent antiresorptive agent, in the present study we investigated the effects of androgen deficiency and subsequent testosterone and estradiol treatment on CT-producing thyroid C cells, skeletal and hormonal changes in middle-aged orchidectomized (Orx) rats. Fifteen-month-old male Wistar rats were either Orx or sham-operated (SO). One group of Orx rats received 5 mg kg(-1) b.w. testosterone propionate (TP) subcutaneously, while another group was injected with 0.06 mg kg(-1) b.w. estradiol dipropionate (EDP) once a day for 3 weeks. A peroxidase-antiperoxidase method was applied for localization of CT in the C cells. The studies included ultrastructural microscopic observation of these cells. The metaphyseal region of the proximal tibia was measured histomorphometrically using an imagej public domain image processing program. TP or EDP treatment significantly increased C cell volume (Vc), volume densities (Vv) and serum CT concentration compared with the Orx animals. Administration of both TP and EDP significantly enhanced cancellous bone area (B.Ar), trabecular thickness (Tb.Th) and trabecular number (Tb.N) and reduced trabecular separation (Tb.Sp). Serum osteocalcin (OC) and urinary Ca concentrations were significantly lower after these treatments in comparison with Orx rats. These data suggest that testosterone and estradiol treatment in Orx middle-aged rats affect calcitonin-producing thyroid C cells, which may contribute to the bone protective effects of sex hormones in the rat model of male osteoporosis.

Sex differences in the regulation of body weight

Obesity and its associated health disorders and costs are increasing. Males and females differ in terms of how and where body fat is stored, the hormones they secrete in proportion to their fat, and the way their brains respond to signals that regulate body fat. Fat accumulation in the intra-abdominal adipose depot is associated with the risk for developing cardiovascular problems, type-2 diabetes mellitus, certain cancers and other disorders. Men and postmenopausal women accumulate more fat in the intra-abdominal depot than do pre-menopausal women, and therefore have a greater risk of developing metabolic complications associated with obesity. The goal of this review is to explore what we know about sexual dimorphisms in adipose tissue accrual and deposition. Elucidating the mechanisms by which sex hormones may modulate the way in which fat is accumulated and stored is a critical area of research due to the prevalence of obesity and the metabolic syndrome, and the rapid increase in propensity for these diseases following menopause.

The cyclic AMP-dependent protein kinase A pathway is involved in progesterone effects on calcitonin secretion from TT cells

It is well known that gonadal steroid hormones influence the level of plasma calcitonin (CT), but the mechanism by which progesterone affects CT secretion is not clear. Immortalized TT cells are a reliable model system for studying the endocrine function of human parafollicular cells. In the present study, the effects of progesterone on CT secretion were examined in TT cells. TT cells were incubated in medium containing vehicle (DMSO), progesterone or BSA-progesterone for 60 or 150 min, and then the levels of CT in the medium, progesterone receptors, cAMP accumulation and CT mRNA expression were measured. To study the correlation between progesterone effects and the cAMP-dependent protein kinase A (PKA) pathway, cell lysates or cells in 24-well plates were treated with either vehicle or progesterone plus RU486, SQ22536, KT5720, or 3-isobutyl-1-methylxanthine. Then, adenylyl cyclase and protein kinase A (PKA) activities were measured in the cell lysates, and the CT levels were measured in the medium from the 24-well plate. The activated cAMP response element binding protein (P-CREB) was also measured by immunofluorescence. Administration of 1 microM progesterone or 500 nM BSA-progesterone increased the secretion of CT by 381% and 100%, respectively. Progesterone receptors A and B were downregulated by progesterone treatment. The cAMP concentration, adenylyl cyclase and PKA activity, CT mRNA expression, and nuclear P-CREB concentrations all showed an increase after progesterone treatment. RU486, SQ22536 and KT5720 inhibited the progesterone-stimulated effects. These results suggest that a cAMP-dependent PKA pathway is involved in progesterone-stimulated effects on CT secretion from TT cells.

Identification of Calcitonin Expression in the Chicken Ovary: Influence of Follicular Maturation and Ovarian Steroids1

Calcitonin (CALCA), a hormone primarily known for its role in calcium homeostasis, has recently been linked to reproduction, specifically as a marker for embryo implantation in the uterus. Although CALCA expression has been documented in several tissues, there has been no report of production of CALCA in the ovary of any vertebrate species. We hypothesized that the Calca gene is expressed in the chicken ovary, and its expression will be altered by follicular maturation or gonadal steroid administration. Using RT-PCR, we detected Calca mRNA and the calcitonin receptor (Calcr) mRNA in the granulosa and theca layers of preovulatory and prehierarchial follicles. Both CALCA and Calca mRNA were localized in granulosa and thecal cells by confocal microscopy. Using quantitative PCR analysis, F1 follicle granulosa layer was found to contain significantly greater Calca mRNA and Calcr mRNA levels compared with those of any other preovulatory or prehierarchial follicle. The granulosa layer contained relatively greater Calca and Calcr mRNA levels compared with the thecal layer in both prehierarchial and preovulatory follicles. Progesterone (P(4)) treatment of sexually immature chickens resulted in a significantly greater abundance of ovarian Calca mRNA, whereas estradiol (E(2)) or P(4) + E(2) treatment significantly reduced ovarian Calca mRNA quantity. Treatment of prehierarchial follicular granulosa cells in vitro with CALCA significantly decreased FSH-stimulated cellular viability. Collectively, our results indicate that follicular maturation and gonadal steroids influence Calca and Calcr gene expression in the chicken ovary. We conclude that ovarian CALCA is possibly involved in regulating follicular maturation in the chicken ovary.

Expression of sex steroid hormone receptors in C cell hyperplasia and medullary thyroid carcinoma

Previous studies have shown that C cells are twice as numerous in male than in female thyroids and that C cell hyperplasia (CCH) is much more frequent in men. These findings suggest regulation involving sex steroid hormones through the expression of sex steroid hormone receptors on C cells. To investigate this hypothesis, we performed an immunohistochemical study of estrogen receptors alpha (ER alpha) and beta (ER beta), progesterone receptors (PR), and androgen receptors (AR) on specimens from a series of 40 patients operated on for a medullary thyroid carcinoma (MTC; n=28; female 18, male 10) and/or CCH (n=19; female 6, male 13). ER beta was the only receptor to be consistently expressed in CCH (100%) and MTC (96.5%), whereas ER alpha was never expressed. PR and AR were rarely expressed in MTC (7 and 14%, respectively). AR was expressed in half the CCH cases (53%), with a trend to male predominance (61% in men vs 33% in women). Our study is the first to describe ER beta expression in CCH. In addition, our findings suggest that CCH, and possibly MTC, might be influenced by sex steroid hormones, namely, estrogens and androgens, through the expression of ER beta and AR on C cells.

C-cell hyperplasia

Routine calcitonin assay programs and recent studies on the natural history of familial medullary thyroid carcinoma (MTC) have greatly added to our understanding of C-cell hyperplasia (CCH) and refined its classification. This article is an update on CCH physiopathology related to clinical presentation. With this combined approach, two types of CCH that differ by their physiological characteristics can be identified: neoplastic CCH and reactive (also called physiological) CCH. Neoplastic CCH is caused by a germline mutation of the RET protooncogene in a multiple endocrine neoplasia type 2 (MEN 2) syndrome. It progresses to MTC following a time line that depends on the RET mutation involved. CCH may actually be a misnomer for a neoplastic condition that some authors have proposed to call "in situ-MTC". Reactive CCH is considered to be caused by a stimulus that is external to the C-cell, and its premalignant potential is not documented. Many situations such as hypercalcemia, hyperparathyroidy, chronic lymphocytic thyroiditis or follicular tumors have been associated with reactive CCH, the pathogenesis of which remains unclear. But C-cell density in normal patients is subject to important variability, and several studies have demonstrated the dramatic male predominance in physiological CCH when hypercalcitoninemia was a random discovery. These data suggest that a number of conditions which were previously associated with reactive CCH might be purely fortuitous. Our clinical/pathological confrontation contributes to appropriately distinguishing between various CCH types, and in turn to identify the best way of managing patients.

Possible direct induction by estrogen of calcitonin secretion from ultimobranchial cells in the goldfish

The plasma level of calcitonin (CT), a calcium (Ca)-regulating hormone, is known to increase in female teleosts during the reproductive period. In the present study, a correlation between plasma CT and Ca and one between plasma CT and the gonad somatic index were demonstrated in the female goldfish but not in the male. To clarify the relationship between CT and Ca, we examined the plasma CT and Ca levels after injecting immature goldfish with estrogen. At day 1, the plasma CT level significantly increased, whereas the plasma Ca level was not changed from its initial level. This result suggests that the trigger of CT secretion is estrogen and that estrogen directly acts on the ultimobranchial gland (UBG), a CT-secreting organ. To determine whether the UBG is equipped with estrogen receptor (ER), an ER binding assay and immunohistochemical staining of UBG cells with an antibody against ER were conducted. As a result, estrogen-specific binding (Kd, 18.52 nM; Bmax, 1.35 pmol/mg protein) and ER-immunoreactivity in the UBG were demonstrated. Furthermore, the expression of alpha, beta, and gamma types of ER in the UBG was also detected by use of the reverse-transcription polymerase chain reaction. Thus, we concluded that estrogen acts on the UBG to induce the release of CT, which in turn plays an important role in reproduction directly and/or indirectly through Ca. This is the first report on the existence of ERs in a teleost UBG and the occurrence of CT secretion caused by estrogen.

The thyroid C cells of ovariectomized rats treated with estradiol

The structure and function of thyroid C cells were studied in ovariectomized (Ovx) adult female rats without and after chronic treatment with estradiol dipropionate (EDP). A peroxidase-antiperoxidase method was applied for localization of calcitonin (CT) in the C cells. Morphometric changes in their volume, nuclei, and relative volume density were evaluated in comparison with sham-operated control rats using a stereological method. The number of C cells was calculated. CT content in the sera was determined by radioimmunoassay. Ovariectomy (Ovx) led to a 21% increase in body weight ( P<0.005), while treatment of Ovx rats with EDP decreased body weight by 25% ( P<0.01). The immunoreactivity for CT in C cells of the Ovx rats was markedly increased. Significant decreases in the volume of C cells (by 13%; P<0.05) and serum CT (by 45%) were recorded, while the C cell number increased by 59% ( P<0.05) in relation to the corresponding controls. The treatment of Ovx rats with EDP caused conspicuous degranulation of the C cells. The cellular volume was increased by 11% and serum CT by 36% in comparison with Ovx animals. At the same time a decrease in C cell number by 29% ( P<0.05) was evident. It may be concluded that estradiol deficiency after Ovx reduced the synthesis and release of CT, while chronic treatment of these animals with EDP had a positive effect on the secretory activity of thyroid C cells.

C-cell hyperplasia and medullary thyroid carcinoma: clinicopathological and genetic correlations in 66 consecutive patients

Routine calcitonin (CT) assay programs and genetic testing for RET proto-oncogene mutations have consistently modified the management and understanding of C-cell proliferative disorders. We report a series of 66 consecutive patients with C-cell hyperplasia (CCH) or medullary thyroid carcinoma (MTC) observed in our institution within an 8-year time period. All the patients had a preoperative basal CT assay and an RET proto-oncogene sequencing. Seventeen patients (F-M ratio: 8:9, mean age: 29.7 y) had a multiple endocrine neoplasia Type 2: 3 children <10 years of age had CCH only, and 14 patients had an MTC, with neoplastic CCH in 10/14 cases. Twenty-seven patients (F-M ratio: 18:9, mean age: 56.6 y) had a sporadic MTC, with physiological CCH in 8 and neoplastic CCH in 3 cases. Twenty-two men (mean age: 46.2 y) had CCH only (physiological CCH in 17 men and neoplastic CCH in 5). We conclude that (1) clinical and pathological characteristics (familial MTC, tumor multifocality, neoplastic CCH) usually associated with hereditary MTC may be misleading and that on the contrary, RET sequencing gives no false positive result; (2) sporadic neoplastic CCH accompanies (and probably precedes) a number of sporadic MTC; and (3) women presenting with a sporadic elevated basal CT have a 100% risk of having an MTC (15/15), but this risk is 3-fold less in men (31%), who will most often have CCH only (69%).

Age-related differences in the secretion of calcitonin in male rats

The mechanism of hypercalcitoninemia associated with aging was investigated in male rats. To mimic some of the hormonal changes with aging, orchidectomized (Orch) and hyperprolactinemic rats were used to mimic the physiological status of aging. Orch and haloperidol-induced hyperprolactinemic rats aged 3, 8, and 17 months were infused with CaCl2 and then bled from a jugular catheter following the CaCl2 challenge. Rat thyroid gland was incubated with Locke's medium at 37 degrees C for 30 minutes. Compared with 8- and 3-month-old rats, 17-month-old rats exhibited the lowest levels of plasma testosterone and the highest levels of plasma prolactin (PRL) and calcitonin (CT). The release of CT in the thyroid glands in vitro was highest in 17-month-old rats. Orchidectomy decreased rat plasma CT and thyroid CT release in vitro. Hyperprolactinemic rats had higher levels of plasma PRL and CT compared with control animals. The release of thyroid CT in vitro was greater in hyperprolactinemic rats. These results suggest that the hypersecretion of CT in 17-month-old rats may be due in part to hyperprolactinemia.

Effects of levonorgestrel-releasing subdermal contraceptive implants on bone density and bone metabolism

A prospective, randomized clinical trial observed the effects of Norplant long-term contraceptive implants and domestic implants similar to Norplant on bone mineral density and bone metabolism in female acceptors for 1 year. Bone mineral density (BMD) and bone mineral content (BMC) of lumbar 2-4 and proximal femur of 61 normal women of child-bearing age were measured by dual energy x-ray absorptiometry (DEXA) before and 12 months after implants insertion in both groups. BMD and BMC of lumbar 2-4 in both groups 12 months after implant insertion significantly increased (p < 0.01); with an average increase of 2.40% and 3.34%, respectively in the Norplant implant group, and 2.75% and 4.47%, respectively in the domestic implant group. Urine hydroxyproline and creatinine ratio (Hop/Cr) in the domestic implant group significantly decreased (p < 0.01). There was no significant differences in the effects on BMD and BMC of lumbar spine and femur and on bone metabolism between the two groups of contraceptive implants (p > 0.05). Levonorgestrel releasing contraceptive subdermal implants were not deleterious to the skeleton in women of child-bearing age. There was no significant effect on achieving maximum bone mass in young women.

Age-related differences in the secretion of calcitonin in female rats

The mechanism that causes hypercalcitonemia in female rats and is associated with aging was investigated. Young (3 mo), adult (8 mo), middle-aged (12 mo), and old (21 mo) rats were infused with CaCl2 and were bled from a jugular catheter after a CaCl2 challenge. To mimic some of the hormonal changes caused by aging, the anterior pituitary (AP)-grafted ovariectomized rats with hyperprolactinemic syndrome were used to mimic the physiological status of aging. The rat thyroid gland was incubated with or without ovine prolactin (oPRL; 40 or 80 ng/ml) at 37 degreesC for 30 min. Old rats possessed the lowest levels of plasma estradiol and progesterone yet had the highest levels of plasma prolactin and calcitonin (CT) compared with young, adult, and middle-aged rats. The basal release of thyroid CT in vitro in thyroid glands gradually increased with age. Compared with cortex (CX)-grafted rats, the AP-grafted rats possessed higher levels of plasma PRL, basal and CaCl2-induced levels of plasma CT, and the release of thyroid CT in thyroid glands. After stimulation with oPRL, the in vitro release of thyroid CT increased in both CX- and AP-grafted rats. These results suggest that the hypersecretion of CT in old rats is due at least in part to hyperprolactinemia.

Effects of ovarian steroid hormones and thyroxine on calcitonin secretion in pregnant rats

In the present study, the roles of ovarian steroid hormones and thyroxine (T4) in regulating the secretion of calcitonin (CT) in pregnant rats were examined. The levels of plasma progesterone, pre- and post-CaCl2 plasma CT, and recovery time of plasma CT and calcium after calcium challenge were greatest in midterm pregnant rats. The levels of basal plasma progesterone, CT, calcium, and recovery time of plasma CT after calcium challenge were less in late pregnant rats, but basal plasma estradiol was highest in late pregnancy. The concentrations of plasma T4 were gradually decreased in rats during pregnancy. Regardless of the presence of estradiol, administration of progesterone in ovariectomized (Ovx) rats resulted in an increase of plasma T4 as well as the basal and calcium-induced secretion of CT. Administration of estradiol alone did not alter the CaCl2-induced levels but decreased the post-CaCl2 levels of plasma calcium in Ovx rats. The basal levels of plasma CT were decreased in Ovx rats treated with T4. These results suggest that the hypercalcitoninemia in midterm pregnant rats is due to an increased secretion of progesterone. Hypocalcitoninemia in late pregnant rats, however, is due in part to lower plasma calcium.

[Changes in sexual hormones and bone metabolism disorder in postmenopausal NIDDM patients]

In the present study the bone mineral content (BMC) was measured with a single photoabsorptionmeter in 31 diabetic menopausal females and 45 normal menopausal females, simultaneously the serum level of estradiol (E2), testosterone (T), parathyroid hormon (PTH) and calcitonin (CT) were measured with radioimmunoassay. The results showed, BMC, E2 and CT in diabetic group were significantly lower than in the control group. The serum level of PTH in diabetic group was significantly higher than in the control group. The multiple regression-analysis showed that chiefly the level of E2 in the diabetic group was closely related with BMC. Serum E2 stimulate directly the osteoblasts for the bone reconstruction and increased the bone tissue sensibility to PTH. CT is the antagonistic hormone of PTH and protects the bone mineralization. Hyperglycemia may cause the damage of ovarium and decreased E2-secretion. The lowered E2 level results in combination with elevated PTH and lowered CT level in serum obviously, in loss of a large amount of bone mineral content and in developing the diabetic osteoporosis.

Effect of estrogen status on bone regulating hormones

The effect of surgically induced menopause and a subsequent estrogen monotherapy on the secretion of calciotropic hormones and serum minerals was evaluated in 11 perimenopausal menstruating women. In seven of them, plasma insulin growth factor-I was also assessed. In the 12th-16th week after bilateral oophorectomy, a decline of serum PTH (p < 0.01) and an increase of calcemia (p < 0.05), phosphatemia (p < 0.05), and IGF-I (p < 0.01) were documented. A subsequent transdermal estrogen substitution (100 micrograms/day for 6 weeks) returned these values to the preoperative range. However, neither the operation nor the estrogen treatment altered calcitonin secretion (basal and calcium stimulated), serum 1,25(OH)2, vitamin D3, or magnesium. The effectiveness of oophorectomy as well as compliance of estrogen substitution was documented by serum estradiol, FSH, and LH response. The results demonstrate a stimulating effect of estrogen on PTH secretion, secondary to an estrogen-induced reduction in plasma calcium. They further demonstrate an inhibitory effect on phosphatemia and IGF-I production, but no effect on calcitonin secretion and vitamin D metabolism.

Steroidal and nonsteroidal "add-back" therapy: extending safety and efficacy of gonadotropin-releasing hormone agonists in the gynecologic patient

OBJECTIVE

To assess the efficacy of various steroidal and nonsteroidal add-back regimes in ameliorating hypoestrogenic side effects of long-term GnRH agonist (GnRH-a) therapy in gynecologic patients.

DESIGN

English language literature review.

PATIENTS

Gynecologic patients administered GnRH-a as therapy for ovarian hyperandrogenism, premenstrual syndrome, dysfunctional uterine bleeding, uterine leiomyomata, and symptomatic endometriosis.

INTERVENTIONS

Steroidal and nonsteroidal add-back regimes including estrogens with progestins, progestins alone, and progestins with organic bisphosphonates in combination with various GnRH-a for > or = 6 months of therapy.

MAIN OUTCOME MEASURES

Vasomotor symptoms, bone density changes, lipid profiles, alterations in presenting symptoms, and disease state.

RESULTS

Estrogens in combination with progestins were efficacious as add-back in the management of ovarian hyperandrogenic states, dysfunctional uterine bleeding, premenstrual syndrome, and leiomyomata. Medroxyprogesterone acetate alone is ineffective as add-back for treatment of endometriosis or leiomyomata. Norethindrone is effective as add-back in the management of endometriosis but not leiomyomata, although high doses alter lipid profiles in an undesirable fashion. Organic bisphosphonates show great promise in preserving bone density without other untoward effects.

CONCLUSIONS

No single add-back regime is appropriate for all gynecologic indications for GnRH-a. Ideal protocols preserve the efficacy of agonists while suppressing associated vasomotor symptoms and bone density loss.

Generation and characterization of a human osteosarcoma cell line stably transfected with the human estrogen receptor gene

Although 17 beta-estradiol (E2) replacement therapy has been shown to be effective in treating postmenopausal osteoporosis, the underlying mechanism remains unclear. The presence of low levels of functional endogenous estrogen receptor (ER) in some osteoblastic cells has been demonstrated, and the suggestion that the abundance of ER may be rate-limiting in the action of E2 on these cells has been made. To study the mechanism of ER in regard to E2-mediated effects, we stably transfected a human osteosarcoma cell line, SaOS-2, with an expression vector, pMV-7-ER, containing the human ER gene. We characterized six of the stably transfected clones. One of the stable clones, SaOS-2-ER, expressed extra copies of ER genes integrated into the genome as detected by Southern blot analysis, showed a significantly increased level of ER mRNA by RT-PCR, and contained an increased level of ER cytosolic protein as detected by an ER-specific EIA. The overexpressed ER was functional and sensitive to E2 in a dose-dependent fashion after transient transfection with a vector containing an estrogen response element (ERE) linked to a chloramphenicol acetyltransferase (CAT) reporter gene. Scatchard analysis revealed a single high-affinity binding site with a Kd similar to values obtained for the ER in MCF-7 breast cancer cells. These SaOS-2-ER cells had altered osteoblast phenotypic features including growth inhibition, decreased basal alkaline phosphatase activity, and decreased IL-6 expression and secretion. In response to E2, a greater than 2-fold increase in TGF-beta 1 mRNA was quantitatively measured in these ER-overexpressing osteoblasts. These cells may provide a sensitive and unique model for understanding the mechanism of E2 and ER in overall bone metabolism.

Effects of progesterone on the metabolism of cancellous bone in young oophorectomized rats

The effects of progesterone on cancellous bone in young rats were evaluated. Fifty female rats aged 90 days were divided into 5 groups: (1) Sham-operated controls (SHAM); (2) oophorectomized (OVX) rats; (3) OVX rats treated with estrogen (OVX+E); 4) OVX rats treated with progesterone (OVX+P); and (5) OVX rats treated with estrogen and progesterone (OVX+EP). After surgery, some animals were treated subcutaneously (s.c.) with 0.5 mg of estradiol dipropionate depot, with 5 mg of hydroxyprogesterone capronate depot, or with both hormones, at intervals of 7 days. After 180 days, the bone mineral density (BMD) and bone histomorphometry of their lumbar vertebrae and serological parameters were measured. In the OVX+P group, the BMD and the bone volume as shown by bone histomorphometry were slightly higher than in the OVX group, but not significantly. These parameters in the OVX+E and OVX+EP groups were significantly higher than in the OVX group. The OVX+P group showed a significant increase in the labeled surface and a decrease of the osteoclast number, compared to the OVX group. The OVX+P group showed increases of serum alkarine phosphatase and osteocalcin. From these results, it can be concluded that progesterone treatment might intensify bone formation and suppress bone resorption on cancellous bone in oophorectomized rats, although progesterone alone does not have a positive effect on BMD and bone volume.

Alternatives to HRT in prevention and treatment

Oestrogen hormone replacement therapy remains the first choice for the treatment and prevention of osteoporosis in postmenopausal women, but for patients who are unsuitable for this therapy, which of course includes men, other satisfactory treatments are available. Several placebo-controlled studies have demonstrated that bisphosphonates and calcitonin prevent bone loss or perhaps increase bone density over 2-3-year periods, and reduce the rate of fracture. It is not known whether these treatments will increase bone density over longer periods of time. Cyclical etidronate has recently become licensed in the UK for use in the treatment of osteoporosis, and it is hoped that other bisphosphonates and intranasal calcitonin will soon be added to the available treatments. Fluoride appears to increase bone density but, at doses above a very narrow therapeutic window, it increases the fracture rate, either because of bone redistribution, formation of poor quality bone or a toxic effect on osteoblasts. At present, fluoride remains a treatment to be used only under expert supervision or within the context of controlled clinical trials. Anabolic steroids may be of value in selected elderly patients with osteoporosis. The patient may be able to contribute to the prevention of osteoporotic fracture by exercising, which will improve dexterity and may have a small effect to increase bone density, and by avoiding the factors that predispose to falls, such as icy paths and excess alcohol. Changes in the diet are unlikely to play a major role in the maintenance of bone density in women living in the Western world.

Estrogen receptors and biologic response in rat parathyroid tissue and C cells

The expression of the PTH and calcitonin genes is dramatically decreased by 1,25(OH)2D3 in vivo, and the PTH gene expression is increased by hypocalcemia. We have now studied the effect of estrogens on the expression of these genes in vivo. 17 beta-Estradiol, given to ovariectomized rats, led to a fourfold increase in PTH mRNA and calcitonin mRNA levels. These effects occurred 24 h after single injections of 37-145 nmol estradiol, or after constant infusions of 12 pmol/d for 1 or 2 wk, where there was no effect on serum calcium levels. The estrogen receptor mRNA was demonstrated in the thyroparathyroid tissue by polymerase chain reaction. The estrogen binding was localized to the parathyroid and C cells by immunohistochemistry. Uterus weight was increased by repeated larger doses (73 nmol/d x 7) of estradiol, but not by the small doses (12 pmol/d for 1 or 2 wk) which were effective on the PTH and calcitonin genes, suggesting a sensitive endocrine effect. These results confirm that the parathyroid and C cells are target organs for estrogen, leading to an increased expression of PTH and calcitonin, which by their combined anabolic effect on bone would help prevent osteoporosis.

Progesterone receptor immunoreactivity in pancreatic endocrine tumors. An immunocytochemical study of 156 neuroendocrine tumors of the pancreas, gastrointestinal and respiratory tracts, and skin

BACKGROUND

The immunoreactivity for progesterone receptors (PR) of the majority of endocrine cells of the human pancreas has prompted the authors to investigate if PR expression is maintained in pancreatic endocrine tumors and is correlated with the main clinicopathologic features of these neoplasms. Furthermore, the study has been extended to other neuroendocrine cells and tumors to determine whether PR immunoreactivity is a common feature of neuroendocrine cells and tumors other than those of the pancreas.

METHODS

One hundred fifty six neuroendocrine tumors of the pancreas, gastrointestinal and respiratory tracts, and skin were immunostained for PR with three different monoclonal antibodies and for estrogen receptors (ER). Additional immunostainings for general neuroendocrine markers and for pancreatic hormones were performed in selected cases.

RESULTS

Nuclear immunoreactivity for PR has been documented in the neoplastic cells of 56 (58.33%) of 96 pancreatic endocrine tumors. PR immunoreactivity was not influenced by the sex and age of the patients or the occurrence of a clinical syndrome related to inappropriate hormone secretion. Tumors synthesizing pancreatic polypeptide, glucagon, and insulin expressed PR in higher percentages (80%, 75%, and 66%, respectively) than those producing other pancreatic hormones or those that were not functioning. Irrespective of the functionally different tumor types, PR immunoreactivity showed a significant correlation (P = 0.0003) with the absence of metastases and the lack of tumor invasion of neighboring organs or of large vessels. As opposed to normal and neoplastic islet cells, the neuroendocrine cells and tumors of the gastrointestinal tract, respiratory tract, and skin did not show any PR immunoreactivity, with the single exception of a typical carcinoid tumor of the lung. ER were not identified in any pancreatic or extrapancreatic neuroendocrine cells or tumors.

CONCLUSIONS

Nuclear PR are immunocytochemically detectable in most pancreatic endocrine tumors and are correlated significantly to the absence of pathologic evidence for malignancy. Conversely, PR expression has not been found in normal and neoplastic endocrine cells and tumors investigated.

Influence of estrogen replacement therapy on endogenous calcitonin production rates

Calcitonin is now a well-accepted therapy for inhibition of bone loss, both in the first years of menopause and in established osteoporosis. However, its exact role in the pathogenesis of that disease as well as the interactions between calcitonin production and estrogen metabolism remain unsolved. In order to clarify the influence of estrogen replacement therapy (ERT) on calcitonin secretory capacity, we measured whole plasma immunoreactive calcitonin basal levels, metabolic clearance rates and production rates in a group of postmenopausal women, before and after a daily intake for 28 days of 0.625 mg/day of conjugated equine estrogens, and again 4 weeks after the withdrawal of that estrogen replacement therapy. No significant changes appeared in immunoreactive calcitonin or immunoreactive calcitonin metabolic clearance rate but the production rate significantly increased over the 28 days (mean +/- SEM, from 21.3 +/- 5.1 pg/ml to 25.2 +/- 5.9 pg/ml, p less than 0.05), and then decreased 4 weeks after therapy was withdrawn to the initial level (17.9 +/- 3.6 pg/ml). We concluded that estrogen replacement therapy significantly increases calcitonin secretory capacity. This confirms the interactions between calcitonin production and estrogen metabolism, and may provide an explanation concerning the mode of action of estrogen replacement therapy in prevention of postmenopausal bone loss.

Alterations of thyroid parafollicular cell organization in aged rats neonatally treated with estradiol

Cellular and subcellular organization of parafollicular cells of aged male Wistar rats (180- and 365-day-old), neonatally (3rd day) treated with a single dose (1 mg) of oestradiol-dipropionate (OeDP), were studied. Based on argyrophil properties of parafollicular cells in control and treated group, two morphometrically distinct cell types were observed (under and over 50 microns 2 of cell area), reflecting distinct functional status of the same cell type. The first signs of hyperplastic changes in parafollicular cells were observed in 180-day-old rats and they were more severe in 365-day-old animals. Morphometric averages for the area of parafollicular cells and nuclei, as well as for the cell number in estradiol-treated animals were higher than in the controls, but these differences were statistically insignificant. However, subcellular organization of parafollicular cells showed that besides the cells with clearly visible characteristics such as control hyperplastic cells, there were parafollicular cells with progressively more abnormalities expressed as myelin-like figures, cytoplasmic cribriform structures and dilated endoplasmic reticulum (ER), demonstrating long-lasting effects of neonatally applied estradiol.

Changes in parafollicular cells of rats neonatally treated with estradiol

The parafollicular cells of male and female rats neonatally (3rd day) treated with a single dose (1 mg) of estradiol dipropionate, and sacrificed in peripubertal (38th day) or adult (80th day) period of life, were investigated. These studies included examinations of silver-stained properties of parafollicular cells, morphometric analyses of both the cells and nuclear area and ultrastructural characteristics. Estradiol treatment led to a significant increase of the cellular and nuclear area (micron 2) in both females and males. Different from intact animals remarkable degranulation and hyperplasia of parafollicular cells were evident in estradiol-treated rats. It may be concluded that this sexual hormone applied in neonatal period has an effect on parafollicular cells expressed up to adult period of life.

Serum bone Gla protein in streak gonad syndrome

Osteoporosis is one of the most common complications of streak gonad syndrome (SGS), however its pathogenesis is still unclear. Bone Gla protein (BGP) has been found to be a serum marker of bone turnover in various metabolic disease states. In the present study serum BGP and alkaline phosphatase (AP) were measured in 13 osteoporotic patients with SGS and in 56 healthy women. Mean (+/- SD) serum BGP levels were normal (7.5 +/- 2.0 ng/ml) in seven patients who had been on estrogen-progestin replacement therapy and became significantly elevated (P less than 0.001) 2 and 3 months after discontinuation of the treatment (15.3 +/- 2.3 and 13.2 +/- 1.0 ng/ml, respectively). Mean (+/- SD) serum AP (207 +/- 65 U/l) showed significant increases (P less than 0.05) 2 months after withdrawal of hormonal substitution (287 +/- 74 U/l). Mean (+/- SD) serum BGP (15.4 +/- 3.5) and AP (287 +/- 49) levels were significantly higher (P less than 0.001 and less than 0.05, respectively) in six patients with SGS who had not been on hormonal substitution. These findings are consistent with those obtained in postmenopausal women suffering from "high remodelling osteoporosis" and suggest that bone turnover in osteoporotic patients with SGS is increased and the skeletal loss is a consequence of accelerated bone loss rather than decreased bone formation.

Effects of medroxyprogesterone acetate on some parameters of calcium metabolism in patients with glucocorticoid-induced osteoporosis

Long-acting medroxyprogesterone acetate (MPA) effect on some important parameters of calcium metabolism in patients with glucocorticoid-induced osteoporosis (GCO) was evaluated. Twelve steroid-dependent asthmatic male patients with GCO were administered 200 mg of MPA (Depo-Provera) intramuscularly, and had fasting serum samples obtained at baseline and at weekly intervals for 5 consecutive weeks. Baseline serum samples were also obtained from 12 control healthy male subjects matched for age. The following measurements were made from each serum sample: osteocalcin (OC), skeletal (SAP) and total alkaline phosphatase (TAP), calcitonin (C), insulin-like growth factor I (IGF1), 1,25-dihydroxyvitamin D and 25-hydroxyvitamin D. Significantly lower baseline serum levels of OC and C were found in the patients with GCO than in controls (P less than 0.001). Following MPA administration in GCO patients statistically significant and sustained increases in OC, SAP and C were noticed during the next 5 weeks. No significant differences in baseline levels for TAP, IGF1, 1,25(OH)2D and 25(OH)D between GCO patients and controls were found, and no significant changes following MPA administration in GCO patients were obtained for these parameters. In conclusion, when administered to patients with GCO, MPA seems to stimulate the osteoblastic activity as suggested by sustained increases in OC and SAP serum levels, and also enhances the C production by the C-cells of the thyroid.

Bone loss during gonadotropin-releasing hormone agonist treatment in girls with true precocious puberty is not due to an impairment of calcitonin secretion

Gonadal steroids drive the significant bone mineral increase that occurs at puberty, while estrogen deprivation in postmenopausal women results in bone mass reduction. We looked for bone mineralization in girls with true precocious puberty (TPP) before and after six months of LH-RH analogs treatment. Calcitonin secretion in these girls were studied too. Bone mineral content (BMC) and BMC/BW ratio (single photon absorptiometry) were measured in seven girls (aged 4.3 to 8.7 years) with TPP before LH-RH agonist therapy (long acting D-Trp6-LH-RH 60 micrograms/kg im every 28 days) was started; the patients were reevaluated after six months of therapy. Before therapy, BMC and BMC/BW were increased for chronological age but appropriate for bone age according to our mineralization normative data. After six months of LH-RH analog administration, 17 beta-estradiol and LH levels were suppressed and BMC and BMC/BW showed a small but significant decrease (respectively -5.4%, p less than 0.02 and -6.3%, p less than 0.02). Basal and calcium stimulated calcitonin levels (total and extractable) did not significantly change during the study period. We conclude that in girls with TPP bone mineralization was increased for chronological age but normal for bone age. The estrogen withdrawal secondary to LH-RH analog therapy caused a reduction in bone mass. Such a bone loss is not due to an impairment of calcitonin secretion.

Physiological and pharmacological regulation of biological calcification

Biological calcification is a highly regulated process which occurs in diverse species of microorganisms, plants, and animals. Calcification provides tissues with structural rigidity to function in support and protection, supplies the organism with a reservoir for physiologically important ions, and also serves in a variety of specialized functions. In the vertebrate skeleton, hydroxyapatite crystals are laid down on a backbone of type I collagen, with the process being controlled by a wide range of noncollagenous proteins present in the local surroundings. In bone, cells of the osteoblast lineage are responsible for the synthesis of the bone matrix and many of these regulatory proteins. Osteoclasts, on the other hand, are continually resorbing bone to both produce changes in bone shape and maintain skeletal integrity, and to establish the ionic environment needed by the organism. The proliferation, differentiation, and activity of these cells is regulated by a number of growth factors and hormones. While much has already been discovered over the past few years about the involvement of various regulators in the process of mineralization, the identification and functional characterization of these factors remains an area of intense investigation. As with any complex, biological system that is in a finely tuned equilibrium under normal conditions, problems can occur. An imbalance in the processes of formation and resorption can lead to calcification disorders, and the resultant diseases of the skeletal system have a major impact on human health. A number of pharmacological agents have been, and are being, investigated for their therapeutic potential to correct these defects.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcitonin and estrogens

Estrogen deficiency is thought to be the main factor leading to postmenopausal osteoporosis (PMO). A role for calcitonin (CT) has been proposed as mediator of estrogen action on bone, and therefore, as pathogenetic factor of PMO. However, this hypothesis is still controversial. To further analyze the relationships between estrogens and CT in PMO, we studied the effects of one-year estro/progesterone therapy on CT secretory reserve, evaluated by a calcium infusion test in 12 postmenopausal women, as compared to 12 placebo treated subjects. In the hormone treated group, blood levels of CT showed a progressive increase during the study and a plateau was reached at 9 months, indicating that CT production achieved a new steady state. Hormonal therapy also significantly improved the CT response to calcium stimulation test. A concomitant increase of vertebral bone mass was observed in the hormone treated women, who also maintained initial bone density of femoral dyaphyses. On the contrary, the placebo treated group continued to lose bone mineral at both sites. Our study demonstrates that estrogens regulate CT secretion in postmenopausal women; thus, CT may be considered a mediator of estrogen action on bone.

Estrogen in prevention and treatment of osteoporosis

Estrogen has clearly been shown to decrease bone loss and frequency of osteoporotic fractures. Calcitonin has been shown in several studies to reduce the rate of bone loss, although no data are yet available demonstrating a reduction in fracture frequency. Studies of osteoporosis intrinsically assume that prevention of further loss, or increments in bone mass, will be associated with declines in fracture recurrence. That may not always be the case. Recent controlled studies in which fluoride was used to increase bone mass in vertebral bodies resulted in no significant decline in fracture recurrence, and there was even a suggestion of increased fracture risk at some sites. Thus further data on calcitonin will be important, even though calcitonin is not expected to alter bone quality as does fluoride. Alternative therapies to calcitonin and estrogen are being investigated in clinical studies since both are currently limited in their use. Because calcitonin currently requires nearly daily injections, estrogen remains the principal agent available for both prevention and treatment in spite of its wide effect on multiple body systems. Bisphosphonates, given continuously or intermittently, appear to be relatively safe oral alternatives to calcitonin. The long-term effects of these agents need to be evaluated in greater detail before they can be recommended for prevention, but a role in therapy of the established disorder seems likely. The skeletal effect of bisphosphonates is also inhibition of bone remodeling and therefore prevention of further bone loss. Thus, they add nothing to the other therapeutic regimens from this perspective and as with calcitonin therapy, documentation of decreased frequency of fracture is lacking. Agents to increase bone mass are purely investigational at this time and many years may elapse before efficacy can be shown for such interventions.

Effective therapy of glucocorticoid-induced osteoporosis with medroxyprogesterone acetate

The effect of long-acting medroxyprogesterone acetate (MPA) on the trabecular bone density in patients with glucocorticoid-induced osteoporosis (GCO) was evaluated. Thirteen steroid-dependent asthmatic male patients with GCO were administered 200 mg MPA intramuscularly at 6-week intervals and 1 g of elemental calcium daily for a period of 1 year. Ten additional matched steroid-dependent asthmatic male patients received 1 g of elemental calcium daily (controls). All 23 patients involved in the study had vertebral trabecular bone densitometry (TBD) by quantitative computed tomography (QCT) at baseline and at 6 and 12 months into the study. A 17% increase in TBD was found in the MPA-treated patients at 1 year (from 68.5 +/- 5 to 80.2 +/- 4 mg K2HPO4/cc) in contrast to the control group who experienced a 21% decrease in TBD during the same period of time (from 80.5 +/- 7 to 63.7 +/- 8 mg K2HPO4/cc) (T = 6.90, P = 0.0001 df = 21). There were no significant changes in other parameters followed during the study in the MPA-treated group (serum calcium, phosphorus, magnesium, PTH, alkaline phosphatase, triglycerides, total and HDL cholesterol, urinary excretion of calcium, phosphate, creatinine) except for a decrease in the serum luteinizing hormone (LH) and testosterone (P less than 0.01) as well as of the hydroxyproline-creatinine ratio (P less than 0.01). The results lend support to the hypothesis of a progesterone-glucocorticoid competitive antagonism at the bone level, though other possibilities can be entertained, and suggest MPA as an effective therapy for glucocorticoid-induced osteoporosis in men.

Vertebral bone loss in menopause

A direct correlation between loss of ovarian function and reduction of bone mass is well established. The incidence of fractures sharply increases with age starting from the menopause. Therefore, it is very important to know the rate of bone loss occurring after menopause, at both trabecular and cortical levels. Several factors may contribute to the reduction of bone mass in menopause. Reduced estrogen secretion results in reduced intestinal calcium absorption, increased bone resorption, and probably a deficient production of calcitonin. Furthermore, in vivo and in vitro experimental data confirm that estrogen failure is associated with histologic changes, mirroring the biochemical changes described in postmenopausal osteoporosis.

Estrogens and progestogens conserve bone in rats deficient in calcitonin and parathyroid hormone

To examine the abilities of estrogens and progestogens to slow bone resorption and conserve bone in ovariectomized rats deficient in calcitonin (CT) or parathyroid hormone (PTH), nine groups of animals with 45Ca-labeled bones were studied for 12 wk. Rats were thyroidectomized (TX), parathyroidectomized (PTX), or given sham neck operations (Sham) and treated orally with either estrogen, 300 micrograms 17 beta-estradiol.kg body wt-1.wk-1; progestogen, 500 micrograms norethisterone acetate.kg body wt-1.wk-1; or placebo (Plac). The TX rats had parathyroid autografts and thyroxine replacement. In all surgical groups, estradiol (E2) and norethindrone (Nor) slowed urinary 45Ca excretion and conserved bone (P less than 0.001). However E2 lowered urinary hydroxyproline more than Nor. Total body Ca values (mg +/- SD) were Sham + Plac, 3,079 +/- 201; Sham + E2, 3,886 +/- 335; Sham + Nor, 3,567 +/- 459; TX + Plac, 3,123 +/- 159; TX + E2, 3,869 +/- 235; TX + Nor, 3,540 +/- 422; PTX + Sham, 3,067 +/- 249; PTX + E2, 3,775 +/- 414; PTX + Nor, 3,635 +/- 467. Importantly, E2 and Nor conserved bone as effectively in TX and PTX groups as in Sham rats, although the PTX rats had slower bone resorption and lower plasma 1,25-dihydroxyvitamin D values (P less than 0.001) than groups with intact parathyroids. We conclude that the effects of estrogens and progestogens to slow bone resorption and conserve bone are independent of CT and PTH. These findings appear relevant to the pathogenesis and treatment of postmenopausal osteoporosis.

Calcitonin reserve in healthy women and patients with postmenopausal osteoporosis

A deficit of immunoreactive calcitonin (iCT) has been found in women with postmenopausal osteoporosis (PM-OP), however, recent studies assessing the monomeric fraction of calcitonin (exCT) do not seem to confirm these findings. We have measured serum levels of iCT by radioimmunoassay (RIA) and exCT (chromatography and RIA) at 0, 5, 10, and 20 minutes after the i.v. infusion of 2 mg calcium/kg body weight in four different groups of women: (1) 12 healthy premenopausal women (HPM), (2) 16 early postmenopausal women (EPM), (3) 16 postmenopausal women within more than 2 years of menopause (LPM), and (4) 24 women with PM-OP. In the HPM group, iCT levels increased significantly 5 and 10 minutes after finishing the calcium infusion (P less than 0.05); this did not occur in the other three groups. The exCT levels in the HPM and LPM groups showed a significantly greater increase than in the EPM and PM-OP groups at 5 minutes (P less than 0.05) and at 10 and 20 minutes (P less than 0.01) after infusion. The behavior of the PM-OP and EPM groups was similar throughout the study. We conclude that there is a calcitonin reserve deficiency in the first years after menopause, which recovers later. This hormone deficiency could explain the accelerated bone loss that takes place at this time of life. The patients with PM-OP also show this deficit, and this may play an ethiopathogenic role in the production of the disease.

Effect of salcatonin given intranasally on early postmenopausal bone loss

OBJECTIVE

To study the effect of salmon calcitonin (salcatonin) given intranasally on calcium and bone metabolism in early postmenopausal women.

DESIGN

Double blind, placebo controlled, randomised group comparison.

SETTING

Outpatient clinic for research into osteoporosis.

SUBJECTS

52 Healthy women who had had a natural menopause two and a half to five years previously.

INTERVENTIONS

The 52 women were allocated randomly to two years of treatment with either salcatonin 100IU given intranasally (n = 26) or placebo (n = 26). Both groups received a calcium supplement of 500 mg daily. Seven of the women receiving salcatonin and six of those receiving placebo left the study before its end.

MAIN OUTCOME MEASURES

Bone mineral content in the spine, the total skeleton, and the forearms after two years of treatment.

RESULTS

Bone mineral content in the spine was significantly higher in the women who had received salcatonin than in those who had received placebo both after one year and after two years of treatment. After one year the difference was 3.8% (95% confidence interval 0.0 to 7.6%) and after two years it was 8.2% (3.8 to 12.6%). In contrast, the bone mineral content in the distal and proximal forearms and in the total skeleton declined similarly in both groups by about 2% each year, and after two years of treatment the differences between the groups were not significant. Biochemical estimates of bone turnover were not affected by salcatonin.

CONCLUSION

The results suggest that salcatonin given intranasally in the dose used prevents bone loss in the spine of early post menopausal women but does not affect the peripheral skeleton.

Salmon calcitonin (Miacalcic) nasal spray in prevention and treatment of osteoporosis

Calcitonin (CT) constitutes one of the major choices for the pharmacologic treatment of postmenopausal and senile osteoporosis. In postmenopausal osteoporosis, CT, analogous to estrogens, determines increase of bone mass, improvement of intestinal calcium absorption and a positivization of calcium balance. Patients treated with CT can also benefit from the analgesic effect of the hormone. Unlike estrogens, these beneficial effects of CT occur with minimal risk and require no routine gynecological monitoring. In addition, CT is completely devoid of toxicity. The only limitations to the use of CT are linked to the frequent parenteral injections and the occurrence of side effects. These limitations can now be overcome by the availability of the new nasal spray preparation, which has been developed for synthetic salmon calcitonin (sCT). The introduction of this new form increases the patients' compliance, and the different pharmacokinetic curtails the side effects, compared to the parenteral administration. At present, one-year controlled studies have been reported, showing a beneficial effect of sCT on bone mass in patients with established osteoporosis. Also, shorter studies demonstrate the analgesic activity of sCT treatment in patients with vertebral crush fractures and bone pain. The improvement in the patients' compliance and the reduction of side effects allow this new CT preparation to be used in the prevention of postmenopausal osteoporosis.

Calcitonin for prevention of postmenopausal bone loss

A 2-year randomised pilot study was conducted in 70 patients to see whether the osteoclast-inhibiting effect of calcitonin would reduce postmenopausal vertebral bone loss. An oestradiol-treated group was included in the study as a positive control since oestrogens are known to be effective. Calcitonin reduced vertebral bone loss in doses above 250 micrograms human calcitonin (50 international units) a week, and at this dose was as effective as oestradiol.

Effects of one-year treatment with estrogens on bone mass, intestinal calcium absorption, and 25-hydroxyvitamin D-1 alpha-hydroxylase reserve in postmenopausal osteoporosis

A double-blind, placebo-controlled study on 21 postmenopausal osteoporotic women was performed in order to assess the effects of 1 year estrogen therapy (Premarin, 1.25 mg/day) on bone mass, intestinal calcium absorption, and mineral metabolism. Bone mineral content (BMC), measured by dual photon absorptiometry on the vertebral bodies and the femoral shaft, increased in both areas, but the changes were more evident at the former site, which is predominantly trabecular (+8.3%, P less than 0.05), than at the latter, which is mainly cortical (+2.6%, P less than 0.05). An improvement of intestinal calcium absorption was also detected at the end of the study (P less than 0.05) in the estrogen-treated group. Parameters of bone metabolism showed a decrease in hydroxyproline/creatinine ratio and osteocalcin, an increase in calcitonin, and no significant changes in parathyroid hormone (PTH) and alkaline phosphatase. Serum 1,25-dihydroxycholecalciferol (1,25(OH)2D3) levels increased after estrogen therapy, whereas 25-hydroxycholecalciferol (25OHD3) remained stable during the study period. Renal 25-hydroxyvitamin D 1 alpha-hydroxylase reserve, assessed by the PTH-stimulation test, showed a more rapid response in producing a 1,25(OH)2D3 peak in the estrogen-treated patients compared with the control subjects. However, estrogens did not induce an absolute improvement in the secretory reserve. This study demonstrates that 1 year treatment with estrogens improves both intestinal calcium absorption and BMC in postmenopausal osteoporotic women. The latter effect appears to be induced by an inhibition of bone resorption, associated to an increased secretion of calcitonin, whereas vitamin D metabolites do not seem to contribute substantially to the mediation of estrogen action on bone.